Method for producing material with high magnetostrictive properties



Patented May 2, 1950 METHOD FOR PRODUCING MATERIAL WITH HIGH MAGNETOSTRICTIVE PROPERTIES Roman Smoluchowski, Pittsburgh, Pa., assignor to General Electric Company, a corporation of New York No Drawing. Application January 30, 1947, $erial No. 725,263

1 Claim. 1

The present invention relates to magnetic materials having improved magnetostriction characteristics and to a process for producing such materials.

Magnetostrictive materials are of considerable importance to the efficient operation of certain types of impulse generating equipment such as ultra-sonic generators, impact device and the like. Such devices utilize the property possessed. by many of the magnetic metals of experiencing a dimensional change when subject to the effect of a magnetic field. When the magnetic field alternates or reverses polarity, the magnetic material will likewise reverse its dimensional change with each half cycle of the alternating magnetic field. When subjected to such a field magnetostrictive materials may be successfully used as vibrators.

The energy output of such devices is a function of the amplitude of vibration which depends upon the specific magnetostriction of the material and the length of the vibrating element where the specific magnetostriction is the dimensional change per unit length of the material when subjected to a magnetic field. I-Ieretofore, increases in output have been limited almost entirely to in-- creasing the length of the vibrating element. Although increases in output may be obtained in this manner, the increased size of the equipment due to lengthening of the vibrating element may be objectionable because of space limitations. Further, ultra-sonic generators operate most advantageously at the natural frequencies of the vibrating elements and the natural frequencies of the elements being determined by such factors as their shape, weight and elastic properties are inversely proportional to the length of the element. Any increase in length of a vibrating element to obtain greater energy output reduces the natural frequency of the element and impairs the directional characteristics of a beam of vibrations or compressional waves being generated thereby. To improve the directional characteristics of the beam i. e. to concentrate the vibration or compressional waves in a parallel path or as nearly parallel as possible it is preferred that the operation of the generator be carried on at the higher natural frequencies. By improving the magnetostrictive properties of materials utilized as the vibrating element higher operational frequencies with improved directional characteristics would be realized in smaller generators.

It is, therefore, a principal object of the present invention to provide magnetic materials having outstanding magnetostrictive properties.

2 Other and further objects of the invention will appear as the description thereof proceeds.

It is well known that single crystals of magnetic materials possess higher degrees of magnetostriction in certain directions in the crystal than in other directions. Such materials are said to have high anisotropy of magnetostriction. In a polycrystalline material, in which individual crystals are oriented at random, magnetostriction has an average value which is lower than the highest magnetostriction in a single crystal. I have found that when such polycrystallline magnetic materials are treated in a particular manner, the magnetostrictive characteristics of the material are improved to such an extent that they closely resemble the magnetostrictive characteristics of single crystals; thus providing material sections possessing unusually high anisotropy of magnetostriction.

The media and process for making the same which I desire to protect herein are specified with particularity in the appended claim and are described in the following specification.

In accordance with one aspect of my invention an exceptional value of specific magnetostriction is obtained in magnetic metals or alloys by sub jecting the metals or alloys to a mechanical working treatment.

Such a treatment induces an orientation of the randomly arranged individual crystals in which the individual crystals tend to align with their directions of high magnetostriction in a common direction.

Specifically, I prefer as a first step to reduce the thickness of the metals or alloys to about 10 to 50% of the final dimension by hot working. Thereafter the metal is reduced to the desired final dimension by cold working. As a crystal arrangement giving improved magnetostrictive properties is largely dependent upon the amount of final cold work applied to the metal or alloy I prefer that the metal or alloy be reduced in thickness by about 50 to during the final working stage.

The successive hot and cold rolling of the magnetic material particularly the rather severe cold rollin rearranges the randomly arranged crystals so that the direction of high magnetostriction in the individual crystals tend to become parallel. Having secured a maximum alignment of the crystals of the metal in this manner, the metal is then cut in convenient pieces parallel to the direction of maximum magnetostriction.

Particularly good results are obtained with nickel. As a first step, I prefer to reduce the thickness of the metal to about .050 to .100 inch by hot rolling. Thereafter, the nickel is further reduced in thickness by cold rolling to about .010 to .025 inch. With such treatment I have found that the crystals of nickel are reoriented so that a direction of maximum magetostriction lies at an angle of about 35 with the direction of rolling. The metal is then cut parallel to the direction of maximum magnetostriction to provide .a material having a high degree of specific magnetostriction.

Excellent values of specific magnetostriction have also been obtained with iron-cobalt vanadium alloys containing about to 80% cobalt and about .5 to 1.5% vanadium the vanadium being added in the percentages described to improve the malleability of the alloy. High values of specific magnetostriction are obtained in ironcobalt-vanadium alloys after a treatment similar to that above described for nickel. In treating these alloys, it is preferable to reduce the thickness of the alloy by hot rolling to about .050 to .100 inch and thereafter, cold roll the .alloy to a final thickness of about .010 to .025 inch. With a treatment such as that just described, ironcobalt-vanadium alloys have unusually high values of specific magnetostriction. However, the direction of high magnetostriction is now at an angle of 45 with the rolling direction. To utilize th maximum specific magnetostriction in the alloy, the alloy material should be cut parallel to a plane at an angle of about 45 with the direction of rolling.

A treatment such as I have just described in connection with nickel provides a specific magnetostriction which is about greater than th average specific magnetostriction of untreated nickel. Iron-cobalt-vanadiumalloys containing .5 to 1.5% vanadium and 20, 36 and 50% cobalt respectively, when treated in accordance with the mode above described for such alloys, provide a specific magnetostriction about greater than th average in the untreated alloys.

Nickel additionally .may be treated by annealing at about 700 to 1100 C. for a time necessary to recrystallize the metal (e. g. /2 to 24 hours) to shift the direction of maximum magnetostriction. Nickel treated in this manner .has its direction of high magnetostriction in the direction of rolling 4 whereas the direction of high magnetostriction remains unchanged in the iron-cobalt-vanadium alloys after a similar annealing treatment.

A magnetostrictive medium such as the abovedescribed iron-cobalt-vanadium alloys containing-20,36 and cobaltrespectively and treated in accordance with my invention will provide an excess of magnetostriction at an angle of 45 with the direction of rolling in .010" thick samples as compared with the average megnetostriction-of the alloy of about 30%. This corresponds to an increase of energy output in a magnetostrictive generator .of to percent.

Although 'I have disclosed my invention specifically in connection with nickel and iron-cobaltvanadium alloys, it is equally applicable to other magnetic metals or alloys to improve their magnetostrictive characteristics.

What I claim as new and desire to secure by Letters Patent of the United States is:

The :method of producing a high degree of magnetostriction in nickel which comprises hot rolling said nickel to reduce its thickness to about .050 to .100 inch, cold rolling the nickel to further reduce its thickness to about .010 to .025 inch and thereafter annealing the nickel at a temperature of from '200" to 1100 C. to recrystallize the nickel and shift the direction of maximum magnetostriction in a direction parallel with the rolling direction.

ROMAN SMOLUCHOWSKI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,112,084 Frey et a1 Mar. 22, 1938 2,166,359 Lakatos July 18, 1939 2,234,968 Hayes et al Mar. 18, 1941 OTHER REFERENCES The Journal of The Iron and Steel Institute, No. 1, 1930, vol. CXXI published by the Institute, London, page 726.

Structure of Metals, Barrett, 1943, McGraw- Hill Book Co., Inc., pages 443, 444 and 460. 

